Displacement-pressure regulator for a casting system

ABSTRACT

A casting system includes a first mold, a second mold, the first mold and the second mold being configured to receive molten metal, the first mold and the second mold exerting pressure on the molten metal to form a mechanical component as the molten metal cools, and a sensor that measures the pressure exerted on the molten metal to provide feedback information to regulate the pressure exerted on the molten metal.

FIELD

The present disclosure relates to a pressure regulator. Morespecifically, the present disclosure relates to a displacement-pressureregulator for a casting system.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Current manufacturing processes for producing engine components of amotor vehicle, for example, cylinder blocks include high pressure diecast (HPDC) processes. Typically, as molten metal is directed to a mold,HPDC high velocity fill processes entrain air, generate oxides and havedifficulty addressing metal shrinkage from certain regions within themold. Other processes include precision sand casting which employs abonded sand core pack mold with a large thermal bulk head chill and headdeck risers to achieve desired material properties. Precision sandcasting, however, is a costly process reserved for components requiringhigh integrity and enhanced material properties.

Accordingly, there is a need in the art for a cost efficient castingprocess for producing high quality and performance cast components.

SUMMARY

The present invention provides a system to cast mechanical components.Accordingly, in one aspect of the present invention, a casting systemincludes a first mold, a second mold, the first mold and the second moldbeing configured to receive molten metal, the first mold and the secondmold exerting pressure on the molten metal to form a mechanicalcomponent as the molten metal cools, and a sensor that measures thepressure exerted on the molten metal to provide feedback information toregulate the pressure exerted on the molten metal.

The foregoing aspect can be further characterized by one or anycombination of the features described herein, such as: the systemfurther includes a pressure punch that receives the feedbackinformation, the pressure punch varying the exerted pressure on themolten metal; the exerted pressure is varied according to a desiredtime-pressure profile; the sensor is a hydraulic pressure sensor; thesensor is a stack of Belleville washers; the system further includes aplurality of slides positioned within the first mold and the secondmold, the positioning of the plurality of slides exerting the directpressure on the molten metal; the plurality of slides is four slides;and each slide is an insert that reciprocates along a respectivechannel.

Accordingly, pursuant to another aspect of the present invention, anapparatus to form a mechanical component includes a first mold, a secondmold, the first mold and the second mold being configured to receivemolten metal, the first mold and the second mold exerting pressure onthe molten metal to form a mechanical component as the molten metalcools, and a feedback mechanism that measures the exerted pressure andvaries the exerted pressure to a desired time-pressure profile.

The foregoing aspect can be further characterized by one or anycombination of the features described herein, such as: the feedbackmechanism includes a sensor that measures the exerted pressure; thefeedback mechanism includes a pressure punch that receives feedbackinformation from the sensor, the pressure punch varying the exertedpressure on the molten metal; the sensor is a hydraulic pressure sensor;the sensor is a stack of Belleville washers; the apparatus furtherincludes a plurality of slides positioned within the first mold and thesecond mold, the positioning of the plurality of slides exerting thedirect pressure on the molten metal; the plurality of slides is fourslides; and each slide is an insert that reciprocates along a respectivechannel.

Accordingly, pursuant to yet another aspect of the present invention, amethod to control a casting process to form a mechanical componentincludes one or more of the following steps: pouring molten metal intoan interior cavity defined by a first mold and a second mold, exertingpressure on the molten metal to form a mechanical component, andmeasuring the exerted pressure and regulating the exerted pressureaccording to a desired time-pressure profile.

The method to control the casting process may be further characterizedby one or any combination of the following features: measuring andregulating the exerted pressure includes measuring and regulating with ahydraulic pressure sensor; measuring and regulating the exerted pressureincludes measuring and regulating with a stack of Belleville washers;and exerting pressure includes exerting pressure with a plurality ofslides positioned within the first mold and the second mold.

Further features, advantages, and areas of applicability will becomeapparent from the description provided herein. It should be understoodthat the description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of the presentdisclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.In the drawings:

FIG. 1 is a perspective view of a top mold and bottom mold for thedirect squeeze casting system in accordance with the principles of thepresent invention;

FIG. 2 is an interior view of the top and bottom molds;

FIG. 3 illustrates the top and bottom molds separately;

FIG. 4 is a schematic view of the system shown in FIG. 1 in use moldinga component;

FIG. 5 is a schematic view of a displacement-pressure regulator systemincorporated into the casting system in accordance with the principlesof the present invention;

FIG. 6 is a graph of a pressure-time plot for the casting system;

FIG. 7 illustrates a Belleville washer stack displacement-pressuresensor for the casting system; and

FIG. 8 illustrates a hydraulic displacement-pressure sensor for thecasting system; and

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring now to the drawings, a direct squeeze system to caststructural components embodying the principles of the present inventionis illustrated therein and designated at 10. Turning in particular toFIG. 1, the system 10 includes a pour cup 12 that communicates with adownsprue or downgate 14, which, in turn, communicates a set of molds 16and 18 through one or more ingates 22. When the system 10 is in use,molten metal 11 is poured into the pour cup 12. The molten metal flowsdown the downgate 14 into the gates 22. Note that in certainarrangements the downgate 14 communicates with a runner that distributesthe molten metal to a plurality of ingates 22. Although no runner andonly one gate 22 is shown in FIG. 1 for the sake of simplicity, itshould be understood that more than one ingate 22 may be employed with arunner. Accordingly, the molten metal 11 flows through the one or moregates 22 into the bottom mold 18. The bottom mold 18 and the top mold 16define a mold cavity or an interior region 28. Hence, as the moltenmetal flows into the bottom mold 18, the molten metal fills the interiorregion 28. As the molten metal in the interior region 28 cools, it formsa structural component 30. The top mold 16 incudes a vent 29 to relievepressure within the interior region 28. Further, a direct pressure punchmay be associated with the vent. That is, the punch may be controlled tovary the hydrostatic pressure in the molten metal as the component 30solidifies. Other processes to fill the molds include tilt pour, lowpressure, and electromagnetic pumps.

In the system 10, the molten metal is poured into the respective systemwith a slow pour velocity. For example, in some arrangements, the pourvelocity through the gates 22 is less than 100 cm/sec, preferably lessthan 50 cm/sec. In contrast, in high pressure die cast (HPDC) systems,the pour velocity exceeds 2000 cm/sec, and, in some arrangements,approaches 3800 cm/sec. A particular benefit of the low speed pourvelocity for the system 10 is the quiescent flow of the molten metal asit flows into the molds 16 and 18, which thereby reduces or eliminatesturbulence in the flowing molten metal. In comparison to HPDC systems,the non-turbulent flow of the molten metal reduces the entrainment ofair in the molten metal, which reduces the creation of structural voidsin the structural component 30. In some arrangements, the surface of theinterior cavity 28 is coated with a pressure sensitive coating, whichenhances heat transfer and directional solidification, since the coatinghas a high thermal resistance with no pressure and low or no thermalresistance with high pressure. An example of such a coating is Trabo™available from REL, Inc.

Generally, molten metal shrinks as it cools. For example, aluminumshrinks about 6% as it solidifies. Another feature of the systems 10 and100, is the ability to compensate for the shrinkage of the molten metalas it cools and solidifies. Specifically, as shown in FIGS. 2 and 3, aset of inserts or slides 32, 34, 36 and 38 are positioned in the top andbottom molds 16 and 18. The slides 32, 34, 36 and 38 are configure toreciprocate along channels 50, 52, 54 and 56 in the top mold 16 andcorresponding channels 68, 70, 72 and 74 in the bottom mold 18 toaccommodate material geometries of the component 30. As such, as themolten metal flows into the interior region 28 defined by a cavity 60 ofthe top mold 16 and a cavity 62 of the bottom mold 18, the slides 32,34, 36 and 38 slide outwardly along their respective channels 50, 52,54, 56 and 68, 70, 72, 74, as indicated by the arrows 40, 42, 44 and 46.As the molten metal cools and shrinks, the slides 32, 34, 36 and 38slide inwardly to compensate for shrinkage of the molten metal as iscools and solidifies to form the metal component 30 (shown as a blockfor the sake of simplicity).

Note also, that the positioning of the top mold 16 and the bottom mold18 exerts or applies controlled direct pressure on the cooling moltenmetal as well. For example, FIG. 4 schematically illustrates pressurebeing directly applied in a controlled manner from six directions (topand bottom and from the sides) to mold the mechanical component 30.Specifically, the top mold 16 can be moved up and down as indicated bythe arrow 66 and the bottom mold 18 can be moved up and down asindicated by the arrow 64, in addition to the direct pressure applied bythe slides 32, 34, 36 and 38 along the lines 40, 42, 44 and 46. Further,the applied pressure can be controlled with the use of theaforementioned pressure punch and the vent 29.

Referring to FIG. 5, there is shown the casting system 10 with apressure sensor/regulator system 71 incorporated into the top mold 16.Specifically, the pressure sensor/regulator system includes one or morepressure sensors 70 and 72 that measures the pressure in the moltenmetal 30 as the molten metal cools and solidifies. The die materialsurrounding sensors 70 and 72 can either be insulated or externallyheated. Insulating or heating the sensors keeps metal in them moltenlonger so they maintain the ability to sense hydrostatic pressure andact as a kinetic riser, thereby feeding the local regions in the castingprocess. This pressure information is fed back to a pressure punch 82positioned in the vent 29 as indicated by the feedback arrows 84 and 85.The sensors 70 and 72 can be associated with displacement regulators asthe molten metal expands and contracts as indicated by the movement(double arrows 78 and 80) of respective pistons 74 and 76.

Hence, when the system 10 is in use, molten metal 30 is poured into theinterior cavity 28 defined by the molds 16 and 18. The pressure punch 82is pressed into the molten metal 30 to apply a desired pressure 100(FIG. 6) while the vent 29 allows gas to escape from the interior cavity28. The pistons 74 and 76 initially move outwards to accommodate themolten metal 30. The pistons 74 and 76 then move inwards to account forcontraction of the molten metal 30 as it cools. In the meantime, thepressure sensors 70 and 72 measure the cavity pressure, which istransmitted back to the pressure punch 82. Accordingly, the appliedpressure is adjusted with the piston punch 82 and the regulators 74 and76 so that the applied pressure 100 provides a desired cavity pressure102.

In sum, the molds 16 and 18 are closed and mechanically locked exceptfor a direct pressure punch detail. Molten metal, such as, for example,aluminum alloy quietly fills the mold cavity with approximately 10%overfill. The mold cavity is vented around the pressure punch or otherlocations. The direct pressure punch sequences shutting off the flow ofmolten metal through the downgate 14 and the ingates 22. The desiredpressure is set and held until the mechanical component 30 solidifies.The molds 16 and 18 are opened and the mechanical component is removed.

The displacement-pressure regulator can provide basic functions duringthe castings process, including providing measurement of internalhydrostatic molten metal pressure for feedback control of pressureapplied by pressure punch(s), and providing repository for excess moltenmetal added to compensate the approximately 6% metal shrinkage whenaluminum alloy transitions from liquid to solid. Note that 6 to 10%excess molten metal is added to the mold cavity to offset the 6% metalshrinkage, and pressure punch(s) and other moving mold slides are ableto move to their dimensional set points and excess metal not used tooffset liquid to solid shrinkage such that casting dimensions are met.Further, excess repository metal can be removed by machining. Moreover,the displacement-pressure regulator enables molten metal displacementrepositories to act as kinetic risers with the ability to feed metalshrinkage in regions with desirable feed-paths to repositories. Kineticrisers are kept active through insulating or externally heating them toallow molten metal in repositories to remain liquid for an extendedperiod of time.

One or both the sensors 70 and 72 can be a stack of Bellville washers 90(FIG. 7) made of individual washers 91 that are configured to enablemovement of the pistons 74 and 76. In other arrangements, one or bothsensors 70 and 72 can be hydraulic pressure sensor 92 (FIG. 8) with acylinder 94 filled with a hydraulic fluid that interacts with a piston96. The piston 96 in turn abuts against the respective pistons 74 and76. In some arrangements, the mold cavity or interior region 28 iscoated with a high thermal resistant-pressure activated coating. Invarious arrangements, the direct squeeze pressure applied to the metalby the system 10 or 100 as it forms the component 30 can vary betweenabout 60 psi to 3000 psi. It should be understood, that the inserts 32,34, 36 and 38 arrangement can be modified for creating differentcomponent geometries. The pressure can be applied directly to astrategic region of the mechanical component 30, for example, the bulkhead region of an engine block. As such, high integrity cylinder blockcastings can be heat treated to optimum tensile and fatigue strengths.Tensile and fatigue strengths of components produced with the system 10or 100 can be at least double as compared to components produced withHPDC systems. Quiescent mold fill combined with low to medium squeezepressure allows for the use of strong sand cores for internal passagesand closed deck designs. Low to medium squeeze pressures can be used todrive molten metal infiltration of ceramic or metal reinforcement oflocal high stress regions of the component. Significantly lower castingpressures reduce tooling and press ruggedness requirements, whichenables the use of simpler casting machines, hydraulic systems andcontrols compared to HPDC machinery. As such, simpler casting machines,hydraulics and controls and improved tool life lowers the cost percomponent compared to components made with HPDC systems.

The description of the invention is merely exemplary in nature andvariations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A casting system comprising: a first mold; a second mold, the firstmold and the second mold being configured to receive molten metal, thefirst mold and the second mold exerting pressure on the molten metal toform a mechanical component as the molten metal cools; and a sensor thatmeasures the pressure exerted on the molten metal to provide feedbackinformation to regulate the pressure exerted on the molten metal.
 2. Thesystem of claim 1 further comprising a pressure punch that receives thefeedback information, the pressure punch varying the exerted pressure onthe molten metal.
 3. The system of claim 2 wherein the exerted pressureis varied according to a desired time-pressure profile.
 4. The system ofclaim 1 wherein the sensor is a hydraulic pressure sensor.
 5. The systemof claim 1 wherein the sensor is a stack of Belleville washers.
 6. Thesystem of claim 1 wherein mold regions around pressure sensors arethermally insulated or externally heated to maintain molten metal inthem, the molten metal in pressure repositories being the last regionsto solidify so they can sense pressure and act as pressurized kineticrisers from the sensor, and wherein a change in a casting programsequence causes the sensor to initiate pressure instead of sensingpressure.
 7. The system of claim 1 wherein the sensor is part of adisplacement-pressure regulator that provides pressure measurement andfeedback control for repository of any excess metal not consumed duringcompensation of the metal shrinkage during transition from liquid tosolid phase transformation, the repositories being passive or kineticrisers to assist in feeding metal shrinkage.
 8. The system of claim 1further comprising a plurality of slides positioned within the firstmold and the second mold, the positioning of the plurality of slidesexerting the direct pressure on the molten metal.
 9. The system of claim8 wherein the plurality of slides is four slides.
 10. The casting systemof claim 9 wherein each slide is an insert that reciprocates along arespective channel.
 11. An apparatus to form a mechanical componentcomprising: a first mold; a second mold, the first mold and the secondmold being configured to receive molten metal, the first mold and thesecond mold exerting pressure on the molten metal to form a mechanicalcomponent as the molten metal cools; and a feedback mechanism thatmeasures the exerted pressure and varies the exerted pressure to adesired time-pressure profile.
 12. The apparatus of claim 11 wherein thefeedback mechanism includes a sensor that measures the exerted pressure.13. The apparatus of claim 12 wherein the feedback mechanism includes apressure punch that receives feedback information from the sensor, thepressure punch varying the exerted pressure on the molten metal.
 14. Theapparatus of claim 12 wherein the sensor is a hydraulic pressure sensor.15. The apparatus of claim 12 wherein the sensor is a stack ofBelleville washers.
 16. The apparatus of claim 11 further comprising aplurality of slides positioned within the first mold and the secondmold, the positioning of the plurality of slides exerting the directpressure on the molten metal.
 17. The apparatus of claim 16 wherein theplurality of slides is four slides.
 18. The apparatus of claim 17wherein each slide is an insert that reciprocates along a respectivechannel.
 19. A method to control a casting process to form a mechanicalcomponent, the method comprising: pouring molten metal into an interiorcavity defined by a first mold and a second mold; exerting pressure onthe molten metal to form a mechanical component; and measuring theexerted pressure and regulating the exerted pressure according to adesired time-pressure profile.
 20. The method of claim 19 whereinmeasuring and regulating the exerted pressure includes measuring andregulating with a hydraulic pressure sensor.
 21. The method of claim 19wherein measuring and regulating the exerted pressure includes measuringand regulating with a stack of Belleville washers.
 22. The method ofclaim 19 wherein exerting pressure includes exerting pressure with aplurality of slides positioned within the first mold and the secondmold.